Method for scribing substrate of brittle material and scriber

ABSTRACT

A mother glass substrate is continuously heated by a first laser spot LS 1  to a temperature which is lower than a softening point of the mother glass substrate, along a scribe line formation line SL on a surface of the mother glass substrate, along which a scribe line is to be formed, while an area close to the first laser spot LS 1  is continuously cooled along the scribe line formation line SL; and an area which is close to the cooled area and is on an opposite side to the first laser spot LS 1  is continuously heated by a second laser spot LS 2  along the scribe line formation line SL to a temperature which is lower than the softening point of the mother glass substrate.

TECHNICAL FIELD

The present invention relates to a scribing method and a scribingapparatus for forming a scribe line on a surface of a substrate of abrittle material such as a glass substrate, a semiconductor wafer or thelike used for a flat panel display (hereinafter, referred to as the“FPD”) in order to scribe and break the brittle material substrate.

BACKGROUND ART

In this specification, formation of a scribe line on a mother glasssubstrate of a liquid crystal display panel, belonging to glasssubstrates, which is a type of brittle material substrates, will bedescribed.

An FPD such as a liquid crystal display panel or the like, whichincludes a pair glass substrates assembled together, is produced asfollows. A pair of large sized mother glass substrates are assembledtogether, and then each mother glass substrate is scribed and brokeninto glass substrates included in the FPD. For scribing and breakingeach mother glass substrate, a scribe line is formed in advance by acutter on each glass substrate.

Recently, a method using a laser beam for forming a scribe line on asurface of a mother glass substrate has been put into practice.According to a method using a laser beam for forming a scribe line on asurface of a mother glass substrate, as shown in FIG. 6, a laser beam LBis directed from a laser oscillator 61 toward a mother glass substrate50. The laser beam LB directed from the laser oscillator 61 forms anelliptical laser spot LS along a predetermined line for forming a scribeline (hereinafter, referred to as a “a scribe line formation line”) SLon the mother glass substrate 50. The mother glass substrate 50 and thelaser beam LB directed from the laser oscillator 61 are moved withrespect to each other along a longitudinal direction of the laser spotLS.

The mother glass substrate 50 is heated by the laser beam LB to atemperature which is lower than a softening temperature at which themother glass substrate 50 is melted. Thus, a surface of the mother glasssubstrate 50 having the laser spot LS formed thereon is heated withoutbeing melted.

Toward an irradiation area irradiated with the laser beam LB and in thevicinity thereof on the surface of the mother glass substrate 50, acooling medium such as, for example, cooling water can be sprayed from acooling nozzle 62, so as to form a scribe line. On the surface of themother glass substrate 50 irradiated with the laser beam LB, acompression stress is generated by the heating by the laser beam LB, anda tensile stress is generated by the cooling medium sprayed onto thesurface. Thus, a tensile stress is generated in the vicinity of the areawhere the compression stress is generated. Therefore, a stress gradientis generated between the area having the compression stress and the areahaving the tensile stress, based on the respective stresses. On themother glass substrate 50, a vertical crack is formed along the scribeline formation line SL from a notch TR which is formed in advance in anend area of the mother glass substrate 50.

FIG. 7 is a schematic projection showing an irradiation state of thelaser beam LB on the mother glass substrate 50 which is scribed by ascribing apparatus. FIG. 8 is a plan view schematically showing aphysical changing state of the mother glass substrate 50.

The laser beam LB oscillated from the laser oscillator 61 forms anelliptical laser spot LS on the surface of the mother glass substrate50. The laser spot LS has an elliptical shape, for example, having alonger diameter b of 30.0 mm and a shorter diameter a of 1.0 mm. Thelaser beam LB is directed such that the longer axis thereof is along thescribe line formation line SL.

In this case, the laser spot LS formed on the mother glass substrate 50has a higher thermal energy strength in an outer perimeter area thereofthan that in a central portion thereof. Namely, each of the ends of thelaser spot LS in the direction of the longer axis has the maximum energystrength. Such a distribution of thermal energy strength is obtained byconverting a Gaussian distribution of thermal energy strength.Accordingly, the thermal energy strength is maximum at each of the endsin the direction of the longer axis which is located on the scribe lineformation line SL. The thermal energy strength in the central portion ofthe laser spot LS interposed between the ends is lower than the thermalenergy strength at each of the ends.

The mother glass substrate 50 can relatively move along the direction ofthe longer axis of the laser spot LS. Accordingly, the mother glasssubstrate 50 is first heated with a high thermal energy strength at oneof the ends of the laser spot LS, next heated with a low thermal energystrength in the central portion of the laser spot LS, and then heatedwith a high thermal energy strength while moving along the scribe lineformation line SL. After that, the cooling water from the cooling nozzle62 is sprayed toward an area corresponding to an end of the laser spotLS, for example, a cooling point CP on the scribe line which is awayfrom the end of the laser spot LS by a distance L of 0 to severalmillimeters.

Thus, a temperature gradient is generated between the laser spot LS andthe cooling point CP. As a result, a large tensile stress is generatedin an area opposite to the laser spot LS with the cooling point CPinterposed therebetween. Utilizing this tensile strength, a verticalcrack is generated in the mother glass substrate 50 in a thicknessdirection t from the notch TR formed at an end of the mother glasssubstrate 50 along the scribe line formation line.

The mother glass substrate 50 is heated by the elliptical laser spot LS.In this case, heat is conveyed in the vertical direction from thesurface to the interior of the mother glass substrate 50, with a highthermal energy strength at one end of the laser spot LS. Since the laserspot LS moves relative to the mother glass substrate 50, a portion ofthe mother glass substrate 50 which is heated by a leading end of thelaser spot LS is heated by the low thermal energy strength at thecentral portion of the laser spot LS and then again heated with a highthermal energy strength at a trailing end of the laser spot LS.

Thus, the surface of the mother glass substrate 50 is first heated witha high thermal energy strength, and while the surface of the motherglass substrate 50 is heated with a low thermal energy strength, theheat is conveyed to the interior thereof without fail. At this point,the surface of the mother glass substrate 50 is prevented from beingcontinuously heated with a high thermal energy strength, which protectsthe surface of the mother glass substrate 50 from melting. After that,when the mother glass substrate 50 is heated again with a high thermalenergy strength, the heat permeates into the interior of the motherglass substrate 50 without fail. Thus, a compression stress is generatedon the surface and in the interior of the mother glass substrate 50. Atensile stress is generated by cooling water being sprayed toward thecooling point CP in the vicinity of the area in which the compressionstress is generated.

When the compression stress is generated in the area heated by the laserspot LS and the tensile stress is generated at the cooling point CP bythe cooling water, a large tensile stress is generated in an areaopposite to the laser spot LS with the cooling point CP interposedtherebetween. Such a tensile stress is generated by the compressionstress generated in a thermal expansion area between the laser spot LSand the cooling point CP. Utilizing this tensile strength, a blind crackis generated from the notch TR formed at an end of the mother glasssubstrate 50 along the scribe line formation line.

When the blind crack acting as the scribe line is formed in the motherglass substrate 50, the mother glass substrate 50 is provided to thenext breaking stage. In the breaking stage, a force is applied to bothsides of the blind crack of the mother glass substrate 50 so as togenerate a bending moment, which causes the blind crack to extend in thethickness direction of the mother glass substrate 50. Thus, the motherglass substrate 50 is scribed and broken along the blind crack formedalong the scribe line formation line SL.

With such a scribing apparatus, it is necessary to increase thedifference between the compression stress generated by the laser spot LSand the tensile stress at the cooling point CP, in order to form avertical crack by a stress gradient between the heating by the laserspot LS formed on the surface of the mother glass substrate 50 and thecooling at the cooling point CP. In order to sufficiently perform theheating by the laser spot LS and the cooling by the cooling point CP, itis necessary to reduce the moving speed of the mother glass substraterelative to the laser spot LS and the cooling spot CP. As a result, aproblem occurs in that the formation efficiency of the vertical crack islowered.

In the case where an edge of the mother glass substrate 50, at which theheating by the laser spot LB along the scribe line formation line isstarted, is rapidly heated by an end of the laser spot LS, as shown inFIG. 9( a), there is an undesirable possibility that an uncontrollablecrack CR is formed in the mother glass substrate 50 at a position aheadof the laser spot LS.

At the edge portion of the mother glass substrate 50, a stress remainswhen the mother glass substrate 50 is scribed and broken into apredetermined shape. The residual stress is released by the rapidheating by the laser spot LS, resulting in generation of the crack. Thecrack CR formed at a position ahead of the laser spot LS in this manneris uncontrollable and cannot be formed along the scribe line formationline.

Also in the case where an edge portion of the mother glass substrate 50,at which the heating by the laser spot LS is terminated after a blindcrack BC is formed along the scribe line formation line, is rapidlyheated by an end of the laser spot LS, as shown in FIG. 9( b), there isan undesirable possibility that an uncontrollable crack CR is formedfrom a side surface of the mother glass substrate 50 in a directionopposite to the moving direction of the laser spot LS. This crack CR isuncontrollable and cannot be formed along the scribe line formationline.

The present invention, made to solve these problems, has an object ofproviding a scribing method and a scribing apparatus for forming ascribe line on a brittle material substrate such as a mother glasssubstrate or the like, efficiently and without fail.

Another object of the present invention is to provide a scribing methodand a scribing apparatus for scribing a brittle material substrate whichcan prevent formation of an uncontrollable crack at an edge portion ofthe brittle material substrate.

DISCLOSURE OF THE INVENTION

In a scribing method for a brittle material substrate according to thepresent invention, the brittle material substrate is continuously heatedby a first laser spot to a temperature which is lower than a softeningpoint of the brittle material substrate, along a scribe line formationline on a surface of the brittle material substrate, along which ascribe line is to be formed, while an area close to the first laser spotis continuously cooled along the scribe line formation line; and an areawhich is close to the cooled area and is on an opposite side to thefirst laser spot is continuously heated by a second laser spot along thescribe line formation line to a temperature which is lower than thesoftening point of the brittle material substrate.

The cooled area is longer along the scribe line formation line.

Both sides of the scribe line formation line at an edge portion of thebrittle material substrate are preheated immediately before being heatedby the first laser spot.

Both sides of the scribe line formation line at an edge portion of thebrittle material substrate are preheated while being heated by the firstlaser spot simultaneously.

A scribing apparatus for a brittle material substrate according to thepresent invention is for forming a crack in a surface of the brittlematerial substrate, along which a scribe line is to be formed. Thescribing apparatus includes means for continuously irradiating thebrittle material substrate with a laser beam so as to form a first laserspot, such that an area heated by the first laser spot is heated to atemperature lower than a softening point of the brittle materialsubstrate; means for continuously cooling an area close to the areaheated by the first laser spot along the scribe line formation line; andmeans for continuously irradiating, with a second laser spot, an areawhich is close to the cooled area and is on an opposite side to thefirst laser spot, along the scribe line formation line, such that thearea is heated to a temperature lower than the softening point of thebrittle material substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic plan view showing one exemplary embodiment of ascribing method according to the present invention.

FIG. 2 is a schematic plan view showing another exemplary embodiment ofa scribing method according to the present invention.

FIG. 3 is a front view showing one exemplary embodiment of a scribingapparatus according to the present invention.

FIG. 4 is a schematic plan view showing another exemplary embodiment ofa scribing apparatus according to the present invention.

FIG. 5 is a schematic structural view showing an example of a laseroscillation mechanism used for the scribing apparatus according to thepresent invention.

FIG. 6 is a schematic view illustrating a scribing method using a laserbeam.

FIG. 7 is a projection schematically showing a state of a mother glasssubstrate while a scribe line is being formed by the scribing apparatus.

FIG. 8 is a plan view schematically showing a state of the mother glasssubstrate.

FIGS. 9( a) and 9(b) are each a plan view schematically showing a stateof generation of an uncontrollable crack at an edge portion of themother glass substrate.

FIG. 10 is a schematic plan view showing another exemplary embodiment ofa scribing method according to the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the present invention will be described by way of exampleswith reference to the attached drawings.

A scribing method for a brittle material substrate according to thepresent invention is carried out for example, to form a blind crack,which is to be a scribe line, on a mother glass substrate before themother glass substrate is broken into a plurality of glass substratesincluded in an FPD such as a liquid crystal panel or the like. FIG. 1 isa schematic view of a state of a surface of the mother glass substratewhen the scribing method is carried out.

As shown in FIG. 1, the surface of the mother glass substrate isirradiated with a laser beam, and thus a first laser spot LS1 is formedon the surface along a scribe line formation line SL. At one end of thescribe line formation line SL on the surface of the mother glasssubstrate, a notch is formed in the direction of the scribe lineformation line SL.

The first laser spot LS1 has an elliptical shape, for example, having alonger diameter of 30.0 mm and a shorter diameter of 1.0 mm, and movesin a direction represented by arrow A relative to the surface of themother glass substrate, in the state where a longer axis thereof isalong the scribe line formation line SL.

Along the longer axis of the first laser spot LS1 formed on the surfaceof the mother glass substrate, the thermal energy strength isdistributed as follows; the thermal energy strength is maximum at eachof the ends in the direction of the longer axis, and the thermal energystrength is lower in an intermediate portion between the ends. Theelliptical first laser spot LS1 moves along the scribe line formationline SL on the surface of the mother glass substrate, and sequentiallyheats the scribe line formation line SL.

The first laser spot LS1 heats the mother glass substrate at atemperature which is lower than a softening point at which the motherglass substrate is melted. Thus, the surface of the mother glasssubstrate having the laser spot LS1 formed thereon is heated withoutbeing melted.

On the surface of the mother glass substrate, a small circular coolingpoint CP is formed on the scribe line formation line SL at a positionbehind but close to the first laser spot LS1, the position being behindthe cooling point CP in the advancing direction of the first laser spotLS1. The cooling point CP is formed by a cooling medium such as, forexample, cooling water, compressed air, a mixed fluid of water andcompressed air, He gas, N₂ gas, or CO₂ gas, which is sprayed from acooling nozzle toward the surface of the mother glass substrate. Thecooling point CP is moved along the scribe line formation line SL on thesurface of the mother glass substrate, in the same direction and atsubstantially the same speed as those of the first laser spot LS1 withrespect to the mother glass substrate.

On the surface of the mother glass substrate, a circular or ellipticalsecond laser spot LS2 extending along the scribe line formation line, ata position behind but close to the cooling point CP, the position beingbehind the cooling point CP in the advancing direction of the coolingpoint CP.

In this example, the second laser spot is elliptical.

The second laser spot LS2 has an elliptical shape, for example, having alonger diameter of 30.0 mm and a shorter diameter of 1.0 mm like thefirst laser spot LS1. The second laser spot LS2 moves relative to themother glass substrate, in the same direction and at substantially thesame speed as those of the first laser spot LS1 and the cooling spot CPwith respect to the mother glass substrate. The second laser spot LS2moves in the state where a longer axis thereof is along the scribe lineformation line SL.

Along the longer axis of the second laser spot LS2, the thermal energystrength is distributed as follows like in the case of the first laserspot LS1: the thermal energy strength is maximum at each of the ends inthe direction of the longer axis, and the thermal energy strength islower in an intermediate portion between the ends.

The second laser spot LS2 heats the mother glass substrate at atemperature which is lower than the temperature at which the motherglass substrate is melted, i.e., the softening point of the mother glasssubstrate, while moving relative to the mother glass substrate at a highspeed.

The surface of the mother glass substrate is sequentially heated by thefirst laser spot LS1 along the scribe line formation line SL, and thenthe heated portions are sequentially cooled by the cooling point CP.Then, the cooled portions are sequentially heated by the second laserspot LS2.

Thus, a compression stress is generated by heating with the maximumthermal energy strength at a trailing end of the first laser spot LS1,and a tensile stress is generated when the heated portion is cooled bythe cooling point CP. A stress gradient is generated between the firstlaser spot LS1 and the cooling point CP.

By the generation of the stress gradient between the first laser spotLS1 and the cooling point CP, a blind crack in the vertical direction isgenerated in the mother glass substrate along the scribe line formationline SL.

When the blind crack in the vertical direction is generated along thescribe line formation line SL, the area having the blind crack formedtherein is again heated by the second laser spot LS2. Thus, the verticalcrack formed in the mother glass substrate further extends in thevertical direction and reaches the bottom of the brittle materialsubstrate (the “full body cut” of the brittle material substrate).

The cooling point CP provided between the first laser spot LS1 and thesecond laser spot L82 is not limited to being circular, and may have arectangular shape which is longer along the scribe line formation lineSL as shown in FIG. 2. By the cooling point CP being longer along thescribe line formation line SL, the area heated by the first laser spotLS1 is cooled without fall.

The cooling point CP extending along the scribe line formation line SLis formed by forming the spraying hole of the cooling nozzle throughwhich the cooling medium is sprayed to be rectangular, or by linearlyproviding small circular spraying holes of the cooling nozzle along thescribe line formation line SL.

FIG. 3 is a schematic structural view showing an embodiment of ascribing apparatus for a brittle material substrate according to thepresent invention. The scribing apparatus according to the presentinvention forms, for example, ascribe line for scribing and breaking alarge-sized mother glass substrate into glass substrates used for FPDs.As shown in FIG. 3, this scribing apparatus has a slidable table 12 on ahorizontal base 11. The slidable table 12 is reciprocally movable in aprescribed horizontal direction (Y direction).

The slidable table 12 is supported by a pair of guide rails 14 and 15 soas to be horizontally slidable along the guide rails 14 and 15. Theguide rails 14 and 15 are provided on an upper surface of the base 11and extend in the Y direction, parallel to each other. At a centralposition between the guide rails 14 and 15, a ball screw 13 parallel tothe guide rails 14 and 15 is provided so as to be rotated by a motor(not shown). The ball screw 13 is rotatable both forward and backward. Aball nut 16 is engaged with the ball screw 13. The ball nut 16 isintegrally provided to the slidable table 12 so as not to rotate. Whenthe ball screw 13 rotates forward and backward, the ball nut 16 is movedalong the ball screw 13 in both directions along the Y direction. Thus,the slidable table 12 integral with the ball nut 16 slides in bothdirections along the guide rails 14 and 15 in the Y direction.

A pedestal 19 is horizontally provided on the slidable table 12. Thepedestal 19 is slidably supported by a pair of guide rails 21, which areprovided above the slidable table 12. The pair of guide rails 21 extendin an X direction perpendicular to the Y direction, and are parallel toeach other. At a central position between the guide rails 21, a ballscrew 22 parallel to the guide rails 21 is provided. The ball screw 22is rotatable forward and backward by a motor 23.

A ball nut 24 is engaged with the ball screw 22. The ball nut 24 isintegrally provided to the pedestal 19 so as not to rotate. When theball screw 22 rotates forward and backward, the ball nut 24 is movedalong the ball screw 22 in both directions along the X direction. Thus,the pedestal 19 slides along the guide rails 21 in both directions alongthe X direction.

A rotation mechanism 25 is attached to pedestal 19. On the rotationmechanism 25, a rotatable table 26 is horizontally provided. On therotatable table 26, the mother glass substrate 50, which is to bescribed, is to be placed. The rotation mechanism 25 is structured torotate the rotatable table 26 about a vertical central axis of therotation mechanism 25. The rotation mechanism 25 can rotate therotatable table 26 to an arbitrary rotation angle θ with respect to areference position. On the rotatable table 26, the mother glasssubstrate 50 is secured by, for example, a suction chuck.

Above the rotatable table 26, a support table 31 is provided at anappropriate distance from the rotatable table 26. The support table 31is horizontally supported at a lower end of a first optical holder 33.The first optical holder 33 is vertically provided. An upper end of thefirst optical holder 33 is attached to a lower surface of an attachmenttable 32, which is provided on the base 11. On the attachment table 32,a first laser oscillator 34 for oscillating a first laser beam isprovided. An optical system held inside the first optical holder 33 isirradiated with the laser beam oscillated by the first laser oscillator34.

The laser beam oscillated by the first laser oscillator 34 has aGaussian distribution of thermal energy strength, and is directed by theoptical system provided in the first optical holder 33, such that theelliptical first laser spot LS1 having a predetermined distribution ofthermal energy strength is formed on the surface of the mother glasssubstrate 50 and such that the direction of the longer axis of the firstlaser spot LS1 is parallel to the X direction of the mother glasssubstrate 50 placed on the rotatable table 26.

On the attachment table 32, a second laser oscillator 41 for oscillatinga second laser beam is provided adjacent to the first laser oscillator34. An optical system in a second optical holder 42 provided adjacent tothe first optical holder 33 on the support table 31 is irradiated with alaser beam oscillated from the second oscillator 41. The laser beamoscillated from the second laser oscillator 41 has a Gaussiandistribution of thermal energy strength, and is directed by the opticalsystem provided in the second optical holder 42, so as to form theelliptical second laser spot LS2 having a prescribed distribution ofthermal energy strength on the surface of the glass substrate 50. Thelaser beam is directed in the state where the direction of the longeraxis of the second laser spot LS2 is along the X direction of the motherglass substrate 50 placed on the rotatable table 26 and has anappropriate distance from the first laser spot LS1.

A cooling nozzle 37 is provided on the support table 31 between thefirst optical holder 33 and the second optical holder 42. The coolingnozzle 37 faces the mother glass substrate 50 placed on the rotatabletable 26. The cooling nozzle 37 is for spraying a cooling medium such ascooling water or the like such that the cooling medium forms arectangular shape between the first laser spot LS1 formed by the firstoptical holder 33 and the second laser spot LS2 formed by the firstoptical holder 42, along the longer axis of the first laser spot LS1 andthe second laser spot LS2.

As the cooling nozzle 37, a plurality of nozzles for spraying coolingwater toward a small circular area may be arranged in the X direction,instead of a structure for spraying the cooling water to form arectangular area.

The support table 31 is also provided with a cutter wheel chip 35opposite to the cooling nozzle 37 with the first laser spot LS1 formedby the first optical holder interposed therebetween. The cutter wheelchip 35 faces the mother glass substrate 50 on the rotatable tale 26.The cutter wheel chip 35 is provided in the direction of the longer axisof the first laser spot LS1 formed by the first optical holder 33. Thecutter wheel chip 35 is provided for making a notch in an edge portionof the mother glass substrate 50 placed on the rotatable table 26 alongthe scribe line formation line.

Positioning of the slidable table 12 and the pedestal 19, and control ofthe rotation mechanism 25, the first laser oscillator 34, the secondlaser oscillator 41 and the like are performed by a control section.

The scribing apparatus having the above-described structure forms ablind crack as follows. First, information, including the size of themother glass substrate 50 and the position of the scribe line formationline, at which the scribe line is to be formed, is input to the controlsection.

Then, the mother glass substrate 50 is placed on the rotatable table 26and secured by the suction means. In this state, alignment marksprovided on the mother glass substrate 50 are imaged by CCD cameras 38and 39. The imaged alignment marks are displayed by monitors 28 and 29,and positional information of the alignment marks is processed by animage processing device.

When the rotatable table 26 is positioned with respect to the supporttable 31, the rotatable table 26 is slid in the X direction. Thus, thescribe line formation line at an edge portion of the mother glasssubstrate 50 faces the cutter wheel chip 35. The cutter wheel chip 35 islowered, and a notch is formed at one end of the scribe line formationline of the mother glass substrate 50.

Then, while the rotation table 26 is slid in the X direction along thescribe line formation line, the first laser beam and the second laserbeam are oscillated respectively from the first laser oscillator 34 andthe second laser oscillator 41, and the cooling water is sprayedtogether with compressed air from the cooling nozzle 37. Thus, arectangular cooling point extending along the scribe line formation lineis formed.

The laser beam oscillated from the first laser oscillator 34 forms theelliptical first laser spot LS1 on the mother glass substrate, which islonger along the scanning direction of the mother glass substrate 50,i.e., in the X direction. Behind the laser spot LS1, the cooling pointCP is formed by the sprayed cooling water along the scribe lineformation line. The laser beam oscillated from the second laseroscillator 41 forms, on the mother glass substrate 50, the ellipticalsecond laser spot LS2 which is longer in the X direction behind thecooling point CP.

Owing to the stress gradient between the heating by the first laser spotLS1 and the cooling by the cooling point CP, a blind crack is formed onthe mother glass substrate 50. An area close to the cooling point CP towhich the cooling water is sprayed is heated by the second laser spotLS2, and thus the blind crack which has already been formed is furtherextended deeper toward a rear surface of the mother glass substrate 50.

When the blind crack is formed on the mother glass substrate 50, themother glass substrate 50 is supplied to the next breaking stage. In thebreaking stage, a force is applied to the mother glass substrate 50 suchthat a bending moment acts across the blind crack. Thus, the motherglass substrate 50 is scribed and broken along the blind crack.

As shown in FIG. 4, immediately before an edge portion of the motherglass substrate 50 is irradiated with the first laser spot LS1, eachside of the scribe line formation line may be irradiated and heated witha preheating laser spot LS3. In the case where immediately before thescribe line formation line is irradiated with the first laser spot LS1,both sides of the scribe line formation line at an edge portion of themother glass substrate 50 are heated by the preheating laser spot LS3,the stresses remaining at both sides of the edge portion of the scribeline formation line become substantially the same as each other.Accordingly, even though the edge portion of the mother glass substrate50 is irradiated with the first laser spot LS1 afterwards, formation ofa crack from a side surface of the mother glass substrate 50 to aposition ahead of the first laser spot LS1 in the moving direction ofthe first laser spot LS1 is prevented.

Similarly, immediately before the first laser spot LS1 irradiating themother glass substrate 50 reaches the other edge portion of the motherglass substrate 50, each side of the scribe line formation line may beheated by irradiation of the preheating laser spot LS3. In the casewhere immediately before the first laser spot LS1 reaches the edgeportion of the mother glass substrate 50, both sides of the scribe lineformation line at the edge portion of the mother glass substrate 50 areheated by the preheating laser spot LS3, the stresses remaining at bothsides of the edge portion of the scribe line formation line becomesubstantially the same as each other. Accordingly, even though the edgeportion of the mother glass substrate 50 is irradiated with the firstlaser spot LS1 afterwards, formation of a crack from a side surface ofthe mother glass substrate 50 to a position ahead of the first laserspot LS1 in the moving direction of the first laser spot LS1 isprevented.

The present invention is not limited to the structure in which themother glass substrate 50 is irradiated with a pair of preheating laserspots LS3 immediately before the first laser spot LS1 is directed to themother glass substrate 50 or immediately before the first laser spot LS1reaches the opposite edge portion of the mother glass substrate 50.Alternatively, the mother glass substrate 50 may be continuouslyirradiated with the pair of preheating laser spot LS3 at a positionahead of the first laser spots LS1.

As shown in FIG. 10, the mother glass substrate 50 may be irradiatedwith the pair of preheating laser spots LS3 such that the pair ofpreheating laser spots LS3 are on both sides and parallel to the firstlaser spot LS1.

FIG. 5 is a schematic structural view of a laser irradiation mechanismfor forming a pair of preheating laser spots LS3. In this laserirradiation mechanism, a pair of preheating laser oscillators 71 and 72each oscillate a laser beam. The first preheating laser oscillator 71directs the laser beam in a horizontal direction, and the secondpreheating laser oscillator 72 directs the laser beam downward in avertical direction.

The laser beam oscillated from each of the pair of preheating laseroscillators 71 and 72 is supplied to a shutter 73 which is inclined at45 degrees with respect to the horizontal direction. The shutter 73,when in a light transmissive state, allows a laser beam directed fromthe first preheating laser oscillator 71 in the horizontal direction totransmit therethrough in the horizontal direction. In a light shuttingstate, the shutter 73 reflects, downward in the vertical direction, alaser beam directed from the first preheating laser oscillator 71 whichis in the horizontal direction.

The shutter 73, when in the light transmissive state, allows a laserbeam directed downward from the second preheating laser oscillator 72 totransmit therethrough in the vertical direction. In the light shuttingstate, the shutter 73 reflects a laser beam directed downward from thesecond preheating laser oscillator 72 into the horizontal direction.

Below the shutter 73, a cooling plate 74 is provided. The cooling plate74 is irradiated with the laser beam emitted from the first preheatinglaser oscillator 71 and reflected downward by the shutter 73 and alsowith the laser beam emitted from the second preheating laser oscillator72 and transmitted through the shutter 73.

The laser beam emitted from the first preheating laser oscillator 71 andtransmitted through the shutter 73 in the horizontal direction, and thelaser beam emitted from the second preheating laser oscillator 72 andreflected by the shutter 73 in the horizontal direction, are directed toa twin-spot system lens 75. The lens 75 supplies the pair of laser beamsdirected thereto to a reflective mirror 76 as parallel optical fluxes.Each optical flux supplied to the reflective mirror 76 is reflected bythe reflective mirror 76 and directed to a collection lens 77. Thecollection lens 77 forms a laser spot having a prescribed shape on bothsides of the scribe line formation line on the surface of the motherglass substrate 50.

Where the light transmissive state is “ON” and the light shutting stateis “OFF”, the shutter 73 is switched “ON” or “OFF” at a high speed.

Such a laser irradiation mechanism is located in the scribing apparatusshown in FIG. 3, at a position opposite to the second optical holder 42with the first optical holder 33 interposed therebetween. On both sidesof the scribe line formation line at an edge portion of the mother glasssubstrate 50, preheating laser spots LS3 are formed respectively by apair of laser beams provided by the laser irradiation mechanism.

In this specification, a mother glass substrate of a liquid crystaldisplay panel is described as an example of a brittle materialsubstrate. The present invention provides the same effect in scribingglass substrates assembled together, a single glass substrate, asemiconductor wafer, a ceramic substrate and the like.

The scribing method and the scribing apparatus according to the presentinvention are applicable to scribing of a mother substrate such as aliquid crystal display substrate obtained by assembling glasssubstrates, a transmissive projector substrate, an organic EL element, aPDP (plasma display panel), an FED (field emission display), areflective projector substrate obtained by assembling a glass substrateand a silicon substrate, and the like.

INDUSTRIAL APPLICABILITY

As described above, according to a scribing method and a scribingapparatus for a brittle material substrate of the present invention, asurface of the brittle material substrate such as a mother glasssubstrate or the like is heated by a first laser spot, then cooled, andthen again heated by a second laser spot. Therefore, a blind crack deepin the vertical direction can be formed without fail.

Since an edge portion of the brittle material substrate is preheatedimmediately before being heated by the first laser spot, there is noundesirable possibility that an uncontrollable crack is formed.

1. A scribing method for a brittle material substrate, wherein thebrittle material substrate is continuously heated by a first laser spotto a temperature which is lower than a softening point of the brittlematerial substrate, along a scribe line formation line on a surface ofthe brittle material substrate, along which a scribe line is to beformed, while an area close to the first laser spot is continuouslycooled along the scribe line formation line; and an area which is closeto the cooled area and is on an opposite side to the first laser spot iscontinuously heated by a second laser spot along the scribe lineformation line to a temperature which is lower than the softening pointof the brittle material substrate, wherein both sides of the scribe lineformation line at an edge portion of the brittle material substrate arepreheated with separate preheating spots spaced apart from and onopposite sides of the scribe line immediately before being heated by thefirst laser spot.
 2. A scribing method for a brittle material substrateaccording to claim 1, wherein the cooled area is extended longer alongthe scribe line formation line.
 3. A scribing method for a brittlematerial substrate, wherein the brittle material substrate iscontinuously heated by a first laser spot to a temperature which islower than a softening point of the brittle material substrate, along ascribe line formation line on a surface of the brittle materialsubstrate, along which a scribe line is to be formed, while an areaclose to the first laser spot is continuously cooled along the scribeline formation line; and an area which is close to the cooled area andis on an opposite side to the first laser spot is continuously heated bya second laser spot along the scribe line formation line to atemperature which is lower than the softening of the brittle materialsubstrate, wherein both sides of the scribe line formation line at anedge portion of the brittle material substrate are preheated by separatepreheating spots spaced apart from and on opposite sides of the scribeline while being heated by the first laser spot simultaneously.
 4. Ascribing method for a brittle material substrate according to claim 3,wherein the cooled area is extended longer along the scribe lineformation line.
 5. A scribing apparatus for a brittle materialsubstrate, comprising: heating means for continuously irradiating thebrittle material substrate having a scribe line formation line, alongwhich a scribe line is to be formed, with a first laser beam so as toform a first laser spot, and heating the brittle material substrate to atemperature which is lower than a softening point of the brittlematerial substrate; cooling means for continuously cooling an area closeto an area heated by the first laser spot along the scribe lineformation line; and heating means for continuously irradiating an areawhich is close to the cooled area and is on an opposite side to thefirst laser spot with a second laser beam along the scribe lineformation line so as to form a second laser spot, and heating thebrittle material substrate to a temperature which is lower than thesoftening point of the brittle material substrate, wherein a verticalcrack is formed along the scribe line formation line, the scribingapparatus comprising means for preheating the brittle material substrateat an edge portion of the brittle material substrate by forming a pairof separate preheated spots spaced apart from the scribe line and onboth sides of the scribe line formation line of the brittle materialsubstrate.
 6. A scribing apparatus for a brittle material substrateaccording to claim 5, wherein the cooling means has a structure forspraying a cooling medium such that cooling medium forms a rectangularshape along the scribe line formation line.
 7. A scribing apparatus fora brittle material substrate according to claim 5, wherein the coolingmeans has a plurality of cooling nozzles arranged along the scribe lineformation line, and each cooling nozzle sprays a cooling medium suchthat the cooling medium forms a circular area.
 8. A scribing apparatusfor a brittle material substrate according to claim 5, wherein thepreheating means preheats both sides of the scribe line formation lineat an edge portion of the brittle material substrate immediately beforeheating by the first laser spot.
 9. A scribing apparatus for a brittlematerial substrate according to claim 5, wherein the preheating meanspreheats both sides of the scribe line formation line at an edge portionof the brittle material substrate while being heated by the first laserspot simultaneously.